1. Field of the Invention
This invention relates to an apparatus and method for communicating information using fractional bits-per-symbol signaling rates responsive to communication channel conditions.
2. Description of the Relevant Art
There exist applications for which it is desirable to transmit transmission symbols that each is composed of a number of information bits which may not represent an integer. The signal constellations associated with such transmissions symbols, then, corresponds to non-power-of-two constellation sizes and/or non-integer constellation sizes.
What is needed is a device that affords fractional bits per symbol digital communication approaching a maximum allowable bit rate yet does so in an efficient manner permitting use of compact code sets, or use of a partial response receiver. Before proceeding with a description of exemplary embodiments, it should be noted that the various digital signaling concepts described herein—with the exception, of course, of the inventive concept itself—are all well known in, for example, the digital radio and voiceband data transmission (modem) arts and thus need not be described in detail herein. These include such concepts as multidimensional signaling using 2N-dimensional channel symbol constellations, where N is some integer; trellis coding; fractional coding; scrambling; passband shaping; equalization; partial response; Viterbi, or maximum-likelihood, decoding; Quadrature Amplitude Modulation (QAM); Orthogonal Frequency Division Multiplexing (OFDM), etc.